java.io
Class Console

Methods to access the character-based console device, if any, associated
with the current Java virtual machine.

Whether a virtual machine has a console is dependent upon the
underlying platform and also upon the manner in which the virtual
machine is invoked. If the virtual machine is started from an
interactive command line without redirecting the standard input and
output streams then its console will exist and will typically be
connected to the keyboard and display from which the virtual machine
was launched. If the virtual machine is started automatically, for
example by a background job scheduler, then it will typically not
have a console.

If this virtual machine has a console then it is represented by a
unique instance of this class which can be obtained by invoking the
System.console() method. If no console device is
available then an invocation of that method will return null.

Read and write operations are synchronized to guarantee the atomic
completion of critical operations; therefore invoking methods
readLine(), readPassword(), format(),
printf() as well as the read, format and write operations
on the objects returned by reader() and writer() may
block in multithreaded scenarios.

Invoking close() on the objects returned by the reader()
and the writer() will not close the underlying stream of those
objects.

The console-read methods return null when the end of the
console input stream is reached, for example by typing control-D on
Unix or control-Z on Windows. Subsequent read operations will succeed
if additional characters are later entered on the console's input
device.

Unless otherwise specified, passing a null argument to any method
in this class will cause a NullPointerException to be thrown.

Security note:
If an application needs to read a password or other secure data, it should
use readPassword() or readPassword(String, Object...) and
manually zero the returned character array after processing to minimize the
lifetime of sensitive data in memory.

The bulk read operations read(char[]) ,
read(char[], int, int) and
read(java.nio.CharBuffer)
on the returned object will not read in characters beyond the line
bound for each invocation, even if the destination buffer has space for
more characters. A line bound is considered to be any one of a line feed
('\n'), a carriage return ('\r'), a carriage return
followed immediately by a linefeed, or an end of stream.

args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The number of arguments is
variable and may be zero. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification. The behaviour on a
null argument depends on the conversion.

Returns:

This console

Throws:

IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section
of the formatter class specification.

args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The number of arguments is
variable and may be zero. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification. The behaviour on a
null argument depends on the conversion.

Returns:

This console

Throws:

IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section of the
formatter class specification.

readLine

args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification.

Returns:

A string containing the line read from the console, not
including any line-termination characters, or null
if an end of stream has been reached.

Throws:

IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section
of the formatter class specification.

args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification.

Returns:

A character array containing the password or passphrase read
from the console, not including any line-termination characters,
or null if an end of stream has been reached.

Throws:

IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details
section of the formatter class specification.

Submit a bug or featureFor further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.